The present invention relates generally to smoke detectors, and particularly to a smoke detector configured for detecting both smoldering and fast flaming fires.
Smoke detectors are traditionally designed to provide an early warning by generating a visual and/or audible alarm, while at the same time minimizing nuisance and false alarms. In many instances, techniques used for detecting fast flaming fires are inadequate for detecting smoldering fires and techniques used for detecting smoldering fires are less than desired for detecting flaming fires. In addition, techniques used for detecting both flaming and smoldering fires with one sensor type result in detector thresholds that are overly sensitive and cause excessive nuisance alarms.
Several embodiments exist in the art that are directed to detecting smoldering and fast flaming fires. For example, Wong (U.S. Pat. No. 5,369,397) discloses a smoke detector/alarm that uses a carbon dioxide (CO2) sensor in conjunction with an algorithm that applies a designated one of three possible alarm thresholds depending on the rate of change of sensed CO2 concentration. The smoke detector in Wong is configured for raising the threshold (more insensitive) when ambient CO2 levels are high and lowering the threshold (more sensitive) when ambient CO2 levels are low to avoid nuisance and false alarms. Wong (U.S. Pat. No. 5,103,096) discloses a smoke detector/alarm that uses a CO2 sensor with dual channels for monitoring the rate of change of the ratio of the two channels.
Furthermore, Wong (U.S. Pat. No. 5,966,077) discloses a smoke detector/alarm that uses two sensors—a smoke detector to detect smoldering fires and a CO2 detector to detect fast flaming fires. However, the technology developed by Wong has not achieved commercial success, due in part to the relatively complex technology used to generate the various alarm signals. Another example is Gonzales (US2010/0085199) where the inventor monitors the rate of change of a processed signal and if the rate of change exceeds a preset rate of change, a more sensitive alarm threshold is selected. In Gonzales, additional time is required to generate an alarm condition because of the threshold adjustment.